Treatment of sulfide minerals



Se t; 11, 1962 P. J. MOGAULEY TREATMENT OF SULFIDE MINERALS Filed Jan.21, 1958 FeS OR(FeS+S) ORE HEATING AND +(SI0 +CuS, A928,

SULFUR REMOVAL Au. 2n$,NiS,CoS, etc) ROAST i AIR 0R REDUCING GAIS FeS+SE H20+H2 etc. I LE9! 95'25 9BJEQ"LI' AcTIvATIoN ROAST REDUCING GASFeS+Fe H25 or $02 GAS --I SIO etc. I SULFl-DE SEPARATION 2 PbS,Ag S,

etc. CuS A H2504 FeSQ4 sow- 0 SOLUTION eds NiS, CoS

FeS 0r(Fes+S) IRoN SULFATE 302 AIR 0R OXYGEN DECOMPOSITION F INVENTOR.PATRICK J.MGAULEY BYMM M M /fj/L/ ATTORNEYS United States Patent Office3,053,651 Patented Sept. 11, 1962 3,053,651 TREATMENT OF SULFIDEMINERALS Patrick J. McGauley, Port Washington, N.Y., assignor toChemetals Corporation, New York, N.Y., a corporation of Delaware FiledJan. 21, 1958, Ser. No. 710,255 13 Claims. (Cl. 75-116) This inventionrelates to the treatment of sulfide mineral mixtures containing iron andnon-ferrous metal values. The principal object of the invention is toprovide a method for economically separating the iron, sulfur, andnon-ferrous metal values into commercially desirable products.

Valuable ores containing sulfur, iron, and non-ferrous metals exist insubstantial quantities throughout the world. In the past these ores havebeen subjected to concentration and to various other processes torecover such nonferrous metal values as copper, nickel, cobalt, lead,zinc, cadmium, and so forth. The concentrates have also been treated torecover the contained iron and sulfur. In each case, however, theprocesses used in the past have had the disadvantage of prohibiting theeconomic recovery of all of the components present. The use of suchprior processes has been limited to certain ores and concentrates havinga sufiiciently high concentration of the desired component to make theremoval of that component alone economically feasible.

Various sulfide mineral mixtures can be processed by the process of thisinvention to recover the contained sulfur, iron, and non-ferrous metalvalues. The sulfide mineral mixtures which can be treated include rawsulfide ores as well as partially processed sulfide ores such ascalcines and concentrates. In practice, the sulfide mineral mixturesprocessed according to this invention will be those most readilyavailable and will include such raw ores as pyrrhotite and mixtures ofpyrrhotite with pyrites, as well as non-ferrous metal concentrates suchas copper and nickel concentrates.

The heating of the sulfide mineral mixtures to remove the labile sulfurand also to activate the sulfide mineral mixtures is carried out belowthe melting or fusion point of the mixture. The particular temperatureused will depend mainly upon the type of sulfide mineral mixture beingprocessed. For example, the maximum temperature to which pyrrhotitecontaining little copper could be heated would be about 1073 C., whilethe maximum temperature to which a sulfide mineral mixture containinglarger amounts of copper, such as a copper concentrate, could be heatedwould be approximately 900 C.

This invention provides a process for treating sulfide mineral mixturesto recover in commercially desirable forms the contained iron, sulfur,and non-ferrous metal values. This invention also provides a processwhich can be varied advantageously to recover the sulfur, iron, andother components therefrom in a form which can readily be disposed ofover a wide economic radius.

The term mol ratio of sulfur to iron as used herein means the ratio ofthe sulfur associated with iron and does not include the sulfur presentin sulfide minerals combined with any of the non-ferrous metals. The molratio of sulfur to iron, as can be observed throughout the specificationand particularly in the examples, is the same as the atomic weight ratiobetween the elements. Stated still another way, the mol ratio of sulfurto iron is equal to the weight ratio of 32.066 pounds of sulfur to 55.85pounds of iron.

The term activated calcine is used herein to describe the productproduced by adding metallic iron to a sulfide mineral and heating theresulting mixture containing the metallic iron to a temperature belowthe melting point of ferrous sulfide for a period of time sufiicient toproduce a calcine which has a mol ratio of sulfur to iron of less thanunity and which is capable of being completely dissolved in dilute(about 10%) sulfuric acid with the production of hydrogen sulfide gas.

The term labile sulfur is used herein to describe that sulfur which canbe expelled from sulfide mineral mixtures by heating the sulfide mineralmixtures to a temperature below their melting points in the absence ofan oxidizing agent.

In effecting the transformation of a sulfide mineral from a sulfidemineral mixture containing a mol ratio of sulfur to iron in excess ofunity to an activated calcine containing a mol ratio of sulfur to ironof less than unity it is necessary to add metallic iron to the sulfidemineral mixture. These compositions containing metallic iron, or ahydrogen reducible iron compound, are still considered to be sulfidemineral mixtures having a mol ratio of sulfur to iron in excess of unitysince the metallic iron or hydrogen reducible iron compound present isnot associated with the iron sulfide compounds present. The metalliciron present only becomes associated with the iron sulfide compoundsupon activation of the sulfide mineral mixture as herein described.

The general operating steps of this invention are shown in theaccompanying drawing which is a simplified flow sheet showing theprincipal steps and variations thereof which can be used according tothis invention and which are described in more detail below.

According to this invention sulfide mineral mixtures are first heated toa temperature below the melting point of ferrous sulfide to drive offthe labile sulfur. The sul-' fide compounds remaining after the labilesulfur has been removed may be classified in two groups: (a) thenonferrous metal sulfides, and (b) the iron sulfide compounds. Thesulfide compounds in group (a) are those which correspond to the lowestvalence state of the metal involved. Thus copper sulfide would bepresent as Cu S rather than as CuS. The iron sulfide compound which isstable at these temperatures, however, is not FeS, but is FeS plusexcess sulfur. This excess sulfur is believed to be present in the formof a solid solution of sulfur (or of FeS in the compound FeS, If onlythe iron sulfide compounds are considered, the residual calcine fromwhich the labile sulfur has been removed will still contain a molecularratio of sulfur to iron of up to about 1.15. This molecular ratiocorresponds to the analysis of many pyrrhotite minerals in their naturalstate. Most natural pyrrhotite minerals, in common with the artificialsulfide mixtures resulting from the removal of the labile sulfur frompyritic sulfide minerals are only very slightly soluble in dilute acids.

The non-ferrous sulfide compounds which are stable at temperatures abovethe melting point of ferrous sulfide generally contain sulfur at ratiosapproximately stoichiometric to the lowest valence of the metalinvolved. It is therefore apparent that when a sulfide mineral mixtureis heated to a temperature below the melting point of ferrous sulfide,sulfur will be expelled from both the ferrous and non-ferrous metalsulfides in the mixture.

I have observed that the heating of sulfide mineral mix tures to atemperature below the melting point of ferrous sulfide generally resultsin the production of a sulfide calcine which, when the effect of theknown non-ferrous metal sulfides is subtracted, has a mol ratio ofsulfur to iron of as low as 1.03. Although it may be possible tocontinue to expel sulfur at a temperature below the melting point of FeSuntil the ratio of 1.00 is achieved, this result cannot be achieved inany practical manner unless an oxidizing agent is also present.

The actual heating of the sulfide mineral mixtures to effect the removalof the labile sulfur can be carried out I in the presence of neutralgases, reducing gases, or oxidizing gases and at reduced, atmospheric,or elevated pressures.

If and when all of the sulfur product is desired in the elemental format the location of the plant, or when waste acid solutions or otherextraneous sources of sulfur are available to the process, it will oftenbe desirable to employ reducing gases containing hydrogen in the removalof the labile sulfur according to this invention. When such reducinggases are employed, the labile sulfur in the feed is removed as hydrogensulfide gas.

The labile sulfur can also be advantageously removed from the sulfidemineral mixtures by heating the sulfide mineral mixtures to atemperature below the melting point of ferrous sulfide in the presenceof a gas containing oxygen. When such an oxidizing gas is employed, thelabile sulfur in the feed is removed as sulfur dioxide gas, and it canbe used in those cases where at least part of the sulfur product isdesired in the form of sulfuric acid at the location of the plantemploying this invention. The use of an oxidizing gas to remove thelabile sulfur has the additional advantage that the exothermic heat ofreaction can be employed to heat the sulfide feed, often to the desiredoperating temperature, without the use of any extraneous fuel.

When using an oxidizing gas to remove the labile sulfur from a sulfidemineral mixture, careful control must be exercised to avoid alsooxidizing the desired product to an undesirable extent. Since it is notdifficult to maintain the necessary degree of control, oxidation willoften be the preferred method of removing the labile sulfur.

The removal of the labile sulfur from the sulfide mineral mixturesaccording to this invention not only results in the economic removal ofthis sulfur in commercially desirable and variable forms, but inaddition, permits the economic addition of metallic iron to the sulfidemineral mixtures for subsequent activation to an activated calcinesoluble in dilute sulfuric acid and having a mol ratio of sulfur to ironof less than unity.

It is not absolutely necessary to remove all of the labile sulfur in thelabile sulfur removal step, but it is advantageous to removesubstantially all of the labile sulfur. The presence of labile sulfurincreases the amount of metallic iron necessary for subsequentactivation to a product having a mol ratio of sulfur to iron of lessthan unity since the metallic iron will readily combine with the labilesulfur present.

In addition, it is not essential to stop the removal of sulfur byoxidation when an oxidizing gas is being employed at a point where allof the labile sulfur has been removed, so that the resulting productwill not contain any metal oxides. In fact, the continued oxidation ofthe sulfide mineral mixture to effect a partial oxidation of a smallpart of the ferrous sulfide present to a hydrogen reducible iron oxideis highly advantageous as is hereinafter discussed in more detail. It ishighly desirable, however, to prevent the oxidation of the fen'oussulfide beyond about 2% of the total iron in the original feed. Overoxidation of the ferrous sulfide results not only in excess dilutionwith nitrogen of the sulfur dioxide gas being evolved, but also in theconsumption of excess hydrogen to convert the resulting iron oxide tometal or to the lower valent oxides of iron. Since the amount ofmetallic iron necessary for the subsequent activation treatment isrelatively small, any oxidation of the iron sulfide beyond that requiredfor the activation step has the additional quantities of hydrogen andresults in the production of less H 8 gas during the further processingaccording to this invention.

If a sulfide mineral mixture, such as many natural pyrrhotites,containing only a relatively small amount of labile sulfur is beingprocessed according to this invention, it would not be necessary or evendesirable to treat the sulfide mineral mixture for removal of the smallamount of labile sulfur present. In such a case, the metallic iron orthe hydrogen reducible iron compound required in the subsequentactivation operation to bring the mol ratio of sulfur to iron to belowunity can be added directly to the sulfide mineral mixture according tothis invention. If the original feed already contains metallic iron or ahydrogen reducible iron compound in sufiicient amounts, it, of course,will not be necessary to add the iron to the sulfide mineral mixture andactivation can be carried out directly.

The temperature used to remove the labile sulfur as stated above must bebelow the melting point of ferrous sulfide. I have found that it isadvantageous to maintain the temperature between about 600 C. to about800 C., although temperatures as low as about 450 C. have been found tobe effective when the feed was treated over an excessively long periodof time.

The next step in the process of this invention involves the treatment ofa sulfide mineral to convert the contained iron sulfide into a form thatis completely soluble in dilute sulfuric acid with the generation ofhydrogen sulfide gas. I have found that such sulfide mineral mixtureswhich are relatively insoluble in dilute sulfuric acid can be renderedcompletely soluble therein by mixing particles of metallic iron with theparticles of the sulfide mineral and contacting this mixture for a fewminutes at a temperature below the melting point of ferrous sulfide.

The reacted or activated calcine has a mol ratio of sulfur to iron ofless than unity and is believed to be a solid solution of iron in thecompound FeS. The particles of metallic iron apparently either extractsulfur from the, ferrous sulfide or pyrrhotite or iron is absorbed intothe pyrrhotite or FeS in a manner such that the distribution of sulfurbecomes uniform throughout the resulting product. The resultingactivated calcine is characterized by the ability of its contained ironto dissolve completely in, dilute (10%) sulfuric acid with theproduction of hydrogen sulfide gas.

The minimum quantity of metallic iron which must be added to the sulfidemineral is theoretically equal to the molecular excess of sulfur to ironwhich is associated with the iron in the sulfide mineral. The additionof the minimum theoretical quantity of iron results in an iron product,at equilibrium, which would be the compound FeS. Since the object ofthis invention is the complete dissolution of the iron from the mineralfeed, an excess of iron equal to about 2 mol percent of the total ironin the feed has been found to be advantageous. A sulfide mineral calcinecontaining about 98 percent of its iron as FeS and about 2 percent ofits iron as metal is theoretically the most advantageous activatedcalcine for subsequent use.

The metallic iron can be added to the sulfide mineral in various formsand in various stages of the process of this invention. The addition ofmetallic iron or sponge iron will probably he rarely used in thepractice of this invention. Instead, iron oxide or other hydrogenreducible iron compounds will be added and subsequently reduced duringthe activation step.

The metallic iron or iron oxide can be added to the original sulfidefeed provided this point of addition is economically desirable. It isadvantageous to add the metallic iron or reducible iron compound to theoriginal sulfide mineral feed when the ratio of sulfur to iron issufficiently low that the removal of the labile sulfur is noteconomical.In addition, where the amount of labile sulfur present is low, it is notnecessary to add large quantities of iron or iron oxide. The metalliciron or iron oxide can also be added to the sulfide mineral after thelabile sulfur has been removed. This procedure is best followed wherethe labile sulfur present is in large quantities and where it would beeconomically desirable to remove it prior to the addition of the ironand subsequent activation.

Inv any case, from about 3 to 10 percent, and usually about 5% of thetotal units of iron in the activated product will be generated from ironoxide with a reducing gas or will be added as metal during, or justprior to the activation step.

The next principal step in the process of this invention involves theleaching of the iron from the activated calcine. This leaching operationbroadly involves the mixing of the activated calcine with a dilutesolution of sulfuric acid causing the evolution of hydrogen sulfide gas.The products resulting from the chemical decomposition of the leachingoperation are then separated and collected for further processing. Theleaching of the activated calcine can be carried out in various mannersaccording to this invention, and I have found that it is advantageous toemploy an excess of activated calcine, or a deficiency of sulfuric acid,in the leaching operation.

When excess activated calcine is employed in the leach a neutralsolution of ferrous sulfate is obtained. Since the activated calcine isused in excess, an amount of ferrous sulfide will remain in the residuetogether with the insoluble non-ferrous metal sulfides. The amount offerrous sulfide remaining in the residue will depend upon the amount ofexcess activated calcine employed in the leach and can easily becontrolled. Since one of the objects of this invention is to separatethe iron from the non-ferrous metals, only a small amount of excessactivated calcine will generally be employed in the leach.

When excess activated calcine is employed in the leach the resultingresidue will contain the sulfides of copper, lead, gold, silver, nickel,cobalt, zinc, silica, and the like, provided that these metals arepresent in the sulfide feed being processed.

The ferrous sulfide and all of the Zinc can be removed from the leachresidue by leaching the residue a second time with excess amount of thedilute sulfuric acid. The zinc sulfide present in the residue will reactwith the dilute sulfuric acid to form Zinc sulfate and hydrogen sulfidegas. The resulting leach solution will be a con centrated acidicsolution of zinc sulfate. This acidic solution of zinc sulfate can thenagain be neutralized with an activated calcine containing only zinc andiron sulfides. The chemical reaction involved may be represented by thefollowing reaction equation:

ZnSOq The residue remaining after the zinc has been removed as zincsulfate will still contain the remaining non-ferrous metals. The copper,silver, nickel, and cobalt can be removed from the remaining residue assulfates by several different methods. One advantageous method is tooxidize the copper, silver, nickel, and cobalt sulfides to therespective sulfates with air in a pressurized slurry with dilutesulfuric acid. 7

The copper and silver can be separated from the nickel and cobalt byprecipitation of their sulfides in an acid solution with either hydrogensulfide gas or ferrous sulfide as the source of sulfur. The nickel andcobalt can also be precipitated ash sulfides with ferrous sulfide from aneutral solution. The waste liquors from each of the above separatingsteps can be recycled to the activated calcine leaching system where theadded iron can be recovered.

It will be noted from the above description that the non-ferrous metalsin the feed can be easily separated into at least four separate, andhighly concentrated products, each obtained without importation into thesystem of extraneous chemicals or other precipitants. The four productsso obtained are each at least equal to, if not better than, the usualhigh-grade feed from which the contained metals are generally recoveredby conventional metallurgy. The four solid non-ferrous metalintermediate products will be listed as follows: f r f (1) Leadconcentrate containing'gold and the other precious metals in the feed;

(2) High-grade precipitate of copper sulfide contain- 6 ing the silver,tin, mercury, antimony, etc., when present in the original feed to theprocess;

(3) High-grade chemical precipitate of zinc sulfide containing verylittle iron but most of the cadmium when present in the feed to theprocess; and

(4) High-grade chemical precipitates of nickel and cobalt, essentiallyfree of copper and precious metals.

The two additional products from the leaching and separation system are:

(l) A neutral clarified aqueous solution of ferrous sulfate containingmanganese and other soluble sulfates of similar metals when contained inthe feed; and

(2) A high-grade gas containing principally H 8 and Water vapor but alsocontaining selenium and possibly some arsenic when contained in thefeed.

The selenium may be separated and recovered from the above gas bypreliminary treatment With S0 The sulfur may be recovered in theelemental form by conventional treatment with S0 gas, which is alsoproduced in the process of this invention.

The neutral solution of ferrous sulfate can be further processedaccording to thisinvention in various manners.

One manner of treating the neutral solution of ferrous sulfate accordingto this invention involves the conversion of the neutral solution offerrous sulfate resulting from the activated calcine leach into asolution of sulfuric acid which can be recycled to the leachingoperation and em-i ployed to dissolve more iron from the activatedcalcine.

The regeneration of the acid is accomplished by oxidation of the neutralferrous sulfate to ferric sulfate and ferric oxide, followed byhydrolysis of the ferric sulfate to more ferric oxide and more acid atelevated temperatures according to the following reactions z V When theabove reactions are carried out at a temperature of about 450 F. in thepresence of a small amount of CuSO as a catalyst for the oxidation ofiron, the re action Will proceed to a degree that will yield a solutioncontaining 10 percent H in less than one-half hour of reaction time. Theiron oxide solid must be removed from the acid as soon as possible afterthe solution is cooled to its boiling temperature to avoid the followingreverse reaction which will consume acid:

Fe O -xH O+H SO =Fe (OH) SO Another manner of treating the neutralferrous sulfate solutions produced according to this invention involvesevaporation of the water from the neutral ferrous sulfate solution andthe decomposition of the crystals of ferrous sulfate with pyrites. Thepyrites are employed as a fuel and reducing agent.

The actual quantity of pyrites required depends on the equipmentemployed, but the minimum theoretical quantity which will make thereaction exothermic with air is about 32 mols of iron in pyrites to molsof iron in FeSO -H O crystals. The chemical reactions involved in thisoperation are believed to be about as follows: 50FeSO -H O-l-16FeS +31OPyrite or pyrrhotite are the only fuel-s which, when employed in thisoperation, add both sulfur dioxide to the gaseous sulfur product andiron oxide to the solid iron product. All other fuels will add both COand nitro gen to dilute the sulfur content of the gas and impurities tocontaminate the iron content of the iron oxide. Since I the diluents andimpurities in conventional carbonaceous:

This hydrated iron oxide can then be mixed.

fuels will make both products of this operation less valu able, if notuseless for further processing, this novel use of mineral sulfides as afuel and reducing agent, is an important part of this invention.

Of the two alternates for treating the neutral ferrous sulfate solutionas set forth above the particular alternate selected for any plantinstallation will depend on the feed available to, and the productsdesired from that installation. When the process of this invention isemployed at plants which produce non-ferrous metal sulfides such asnickel, copper, lead and zinc as the primary products, then the firstalternate will generally be desirable. If and when this process isoperated in conjunction with other plants producing more refinedproducts titanium dioxide and normally generating waste acid and/orsulfate salts containing iron, such as pickle liquors, then the secondalternate will generally be desirable.

The following examples illustrate various methods of treating sulfidemineral mixtures for the separation of iron, sulfur, and othernon-ferrous metal values according to this invention.

Example I A sulfide mineral mixture having a mol ratio of sulfur to ironin excess of unity and the following approximate analysis was processedfor the separation of iron, sulfur, and copper according to thisinvention.

calcine was found to be as follows:

Content Component Weight Assumed percent compounds Lbs. Lb.-mols 34.3626 0.87 GU23, 100%. 23. 7 434 7. 77 FeS+Fe, 100%. 21.4 392 12.21 20.6376 Insolubles.

Total 100. 0 1,828 29. B5

The resulting activated calcine was then leached in an excess quantityof 10% sulfuric acid solution resulting in the production of 240 poundsof concentrated hydrogen sulfide gas. The hydrogen sulfide gas wascollected and the resulting leach solution separated from the insolublesby filtration.

Content The residue separated from the solution was dried and Componentan approximate analysis of the residue was found to be Lbs. Lb.-mols asfollows? 31. 3 620 9.87 Content 21. 7 434 7. 77 Component Weight Assumed28. 2 564 17. 26 percent compounds 18. 8 370 LbS. Lb.-mols Total rawconcentrate 100.0 2,000 34.90

Copper 53.6 626 9.87 CuzS. i Iron-.- 0.5 6 0.10 FeSz. The above sulfidemineral mixture was oxidized with i m 162 5 air in a roasting furnace ata temperature of between 376 700 C. to 900 C. until about 30% of thesulfur was re- 40 Total 100.0 1,170 15-02 moved as sulfur dioxide gas.The oxidation of the sulfide mineral mixture resulted in the removal ofabout 30% of the sulfur, produced a sulfide product containing onlythose sulfide compounds of iron and the non-ferrous metals which arestable at temperatures below the melting point of ferrous sulfide and,in addition, resulted in the production of a sufiicient amount of ahydrogen reducible iron compound (Fe O to produce a sulfide mineralactivated calcine having a mol ratio of sulfur to iron of less thanunity when treated according to this invention. The amount of ironpresent as Fe O was equivalent to about 6.5% of the total iron presentin the mixture.

The approximate analysis of the sulfide mineral product resulting fromthe oxidation and removal of about 30% of the sulfur was found to be asfollows:

The compounds in this sulfide mineral calcine were calculated to beapproximately as follows:

Cn Q 100% of the Cu. FeS 93.5% of the Fe. F203 of the Fe.

The above sulfide mineral mixture was then contacted in a suitablefurnace while it was still hot at a temperature of about 700 C. with agas containing hydrogen While The leach solution after being separatedfrom the insoluble residue was then neutralized with excess activatedcalcine to produce a neutral ferrous sulfate leach liquor having thefollowing approximate analysis:

Content Component Weight percent Lbs. Lh.-mols FcSO; 1 402 3.00 H2O etc76 9 1,538 85.44

Total 100. 0 2,000 88. 44

An approximate analysis of the liquid was as follows:

Content Component Weight percent Lbs. Lb.-mols The solid remaining afterthe separation of the liquid was then dried. An analysis of the driedsolid showed that it contained about 98.2% of the iron in the originalfeed and about 1.6% of the sulfur.

The copper residue collected after the leaching of the activated calcinewith dilute sulfuric acid was then further processed to metal byconventional processes. The sulfur in this copper residue was releasedas S during the pro cessing and the S0 combined with the H 8 gas formedduring the leaching of the activated calcine. The total recovery ofsulfur in commercial form was in excess of 89.4% of the sulfur in theoriginal feed.

Example 2 Another ton of the copper sulfide concentrate as set forth inExample I was again processed according to the methods of thisinvention. In this example a dilute acid solution of copper and ironsulfates was available from the leaching of the copper oxide ores, and apyrite mineral concentrate was available from the discarded tailings ofcopper sulfide flotation. The sulfur, iron and copper from all three ofthese products were recovered by the methods of this invention.

The approximate analysis of the copper sulfide con- An approximateanalysis of the acid solution from the copper oxide leaching was asfollows:

Content Component Weight percent Lbs. Lb.-mols Total 100. 0 2, 000.0 92.5

An approximate analysis of the pyrites concentrate from the wastetailings was as follows:

Content Component Weight percent Lbs. Lb.-ruols FeS 91. 0 1, 820 15. 2Acid insolubles 9. 0 180 Total 100.0 2, 000 15. 2

The above copper concentrate feed was heated in the presence of agenerator gas containing about 50% hydrogen in a roasting furnace at atemperature of about 800 C. until about 24.5% of the total sulfur in thefeed was driven off. The total weight of sulfur driven off as hydrogensulfide gas was about 144 pounds. The heating of the sulfide feedresulted in the removal of about 24.5 of the total sulfur in the feed.The sulfur to iron ratio in the remaining product was in excess ofunity, and this product contained only those sulfide compounds of ironand the non-ferrous metals which are stable at temperatures below themelting point of ferrous sulfide.

The approximate analysis of the sulfide mineral mixture resulting fromthe heating thereof in the presence of hydrogen gas was found to be asfollows:

Content Component Weight Assumed percent compounds Lbs. Lb.-mols Copper.33. 8 626 9. 87 Cu S. 23. 4 434 7. 77 FeS+S.

About 80 pounds of Fe O product were recycled from the iron plant andadded to the hot sulfide mineral mixture resulting from the treatmentwith the hydrogen reducing gas, and the resulting mixture was activatedto render the contained iron completely soluble in dilute sulfuric acid,by heating it in a roasting furnace at about 800 C. in the presence of agenerator gas containing about 50% hydrogen. During the heating of thesulfide mineral calcine in the presence of the reducing gas containinghydrogen the mixture was continuously agitated :by raking. The resultingactivated calcine had a mol ratio of sulfur to ironof less than unity,and was completely soluble in dilute (about 10%) sulfuric acid. Theweight, content and approximate analysis of the activated calcine fromone ton of the copper concentrate feed was as follows:

Content Component Weight Assumed percent compounds Lbs. Lb.-mo1s Copper.33. 3 626 9. 87 C1128. [r 24. 6 462 8. 27 FeS+Fe. 22. l 416 13. 00 20.0376 Total 100. 0 1, 880 31. 14

Content Component Weight Assumed percent compounds Lbs. Lb.-mo1sCopper-.. 56.1 832 13.12 Cu S+CuS.

0.9 14 0.25 FeSa. 17.7 262 8.20 Insolubles 25. 3 376 Total 100.0 1, 48421. 67

The approximate analysis of the resulting iron leach solution was asfollows:

Content Component Weight percent Lbs. Lb.-mols Total 100. 0 13, 211 601.25

About 650 pounds of the pyrites concentrate from the waste tailings wasthen added to this iron leach solution and the water present wasevaporated in a spray drier at a temperature of about 80 C. .After thewater was evaporated the resulting product was a homogeneous.

11' mixture of pyrite and FeSO -H O crystals having thefollowingapproximate analysis:

12 The sulfur and copper in the copper sulfide leach residue can berecovered. as sulfuric acid and refined metal respectively byconventional methods. The 81.1%

Content of the sulfur which is removed by the process of this in-Compone t Weight 5- vention is obtained in two gases containingrespectively,

percent Lbmols about 90 volume percent hydrogen sulfide, and about 42.5volume percent sulfur dioxide, each on a dry basis. 77.6 2, 600. 15.32Both or either of these gases can be further processed 91 economicallyto either elemental sulfur or sulfuric acid 17.8 595 5.00

1.0 59 10 by known conventional processes.

Total 100.0 3,345 21.25 Example 3 The above mixture Was en roas ed Withabout 1250 A sulfide mineral mixture having a mol ratio of sulfur Poundsof air at a p 0f ab011t30Q about to iron in excess of unity and thefollowing approximate O 1101113 The approximate analysls 0f the 11011analysis was processed for the separation of iron, sulroaster productswas as ows: fur, and the non-ferrous metals by the methods of thisinvention.

Content Component Weight percent Lbs. Lb.-mols Content Component Weight96. 5 1, 625 1 20. 32 percent 3. 5 59 Lbs. Lb.-mols 4.6 02 1.570 50. 71,680 5. 3 10s 1. 070 33. 5 992 0. 2 4 0. 00s 9. s 202 46. 8 030 16. 78033.7 674 21.000 Total gas 100. 0 2, 904 9. 4 188 The resulting ironoxide product contained only about 3.5 weight percent of totalimpurities, and it will be noted that about 3 times as much iron wasrecovered as was contained in the original copper concentrate feed. Thedifference was extracted from the Waste solutions and the waste pyrites,both of which are generally discarded at copper recovery plants. Theorigin of the total iron in the iron roaster product is shown in thefollowing table:

Feed Component Quantity Lbs./ Weight Lb.

Obs.) F6203 percent mols Fe Copper concentrate 2,000 600 35.6 7. 52Waste liquor.-- 13,000 628 37. 3 7. 80 Waste pyrites-.- 591 397 23. 6 5.00 Dilucnt in pyrite. 59 59 3. 5

Total 15, 650 1, 684 100. 0 20. 32

Feed components Quantity Lbs. Weight Lb.-1nols (lbs) sulfur percentsulfur Copper cone 2, 000 564 40. 2 17. 26 Waste solution 13, 000 52037. 1 16. 28 Waste pyrite 650 320 22. 7 10.00

Total 15, 650 1, 404 100. 0 43. 54

Product compounds Quantity Lbs. Weight Lb.-mo1s (lbs) sulfur percentsulfur H48 from first roast 182 136 9. 8 4. 26 HzS from leach 163 15411. 0 4.80 SO; from second roast- 2, 964 840 60. 3 26. Sulfure in Curesidue- 1, 484 263 18. 9 8.20

Total 4, 793 1, 393 100. 0 43. 51

The above sulfide mineral mixture was mixed with about pounds of Fe Oand the mixture charged to a roaster. The mixture was heated in theroaster to about 750 C. with neutral hot gases from the burning of fueloil.

The resulting product gas contained very little sulfur and was discardedto the atmosphere. The hot sulfide calcine product was fed to a secondroaster countercurrent to a flow of generator gas containing about 50%hydrogen at about 800 C. to reduce the added iron oxide to metalliciron. During the raking of the hot sulfide mineral in the presence ofreducing gas and the Fe O the iron oxide was reduced to metallic iron,and the sulfide mineral mixture was transformed into an activatedcalcine having a mol ratio of sulfur to iron of less than unity andhaving the property of being completely soluble in dilute (about 10%)sulfuric acid.

The resulting activated calcine, after removal from the second roaster,had the following approximate composition:

Content Component Weight Assumed percent compounds Lbs. Lb.-mols 4. 5292 1. 570 bits. 5. 22 106 1. 670 (31128. 0.20 4 0. 068 00S. 49. 10 1,00017.800 FeS +Fe. 31. 70 640 20.030

9. 26 188 SiOz etc.

The above activated calcine was then leached in a recycle solution ofdilute (about 10%) sulfuric acid employing excess calcine. The leachingof the activated calcine resulted in the production of about 575 poundsof concentrated hydrogen sulfide gas and a neutral solution of FeSO Thehydrogen sulfide gas was collected for further processing to elementalsulfur.

13 The composition of the leach residue was approximately as follows:

Content Component Weight Assumed percent compounds Lbs. Lb.-mols 17. 8592 1. 570 NiS. 20.60 106 l. 670 Cars. 0. 78 4 0. 068 C05. 5. 64 29 0.520 FeS. 18. 65 96 3. 000 r 36. 48 188 The above residue was thenoxidation leached with sulfuric acid and air in a pressure vessel at 350F. and 500 p.s.i.g. to produce an acid solution of metallic sulfates.The approximate composition of the acid solution of metallic sulfateswas as follows:

The above slurry was then agitated with hydrogen sulfide gas until allof the copper was precipitated as CuS. The resulting precipitate wasthen removed from the solution and sent to a copper smelter for recoveryof the copper and precious metals content. The approximate compositionof this residue was as follows:

Content Component Weight percent Lbs. Lb.-mols CuS 46.0 160 1. 670Insolubles 54. 0 188 Total 100. 0 348 1. 670

Content Component Weight percent Lbs. Lb.-mols The nickel and cobalt inthe above neutral solution were then precipitated with H 5 gas underpressure. The precipitate was removed by filtration and the liquorcycled to the iron leaching and precipitation system for ironremoval.The composition of the nickel precipitate was approximately as follows:

Content Component Weight percent Lbs. Lb.-mo1s Total 100.0 142 3. 135

Example 4 A sulfide mineral mixture having a mol ratio of sulfur to ironin excess of unity and the following approximate analysis was processedfor the recovery of the non-ferrous metals as sulfides, the iron as anoxide, and the sulfur in elemental form according to the methods of thisinvention.

Content Component Weight percent v Lbs. Lb.-mols 0. 6 12 0. 19 1. 2 240. l2 4. 5 90 1. 38 39. 5 790 14. 15 48. 0 960 30. 00 Insolubles 6. 2124 Total 100.0 2, 000 45. 84

About one-half of the above sulfide mineral mixture was mixed with aboutpounds of FeSO -H O crystals and roasted with air in a roasting furnaceat about 800 C. until about 47% of the total sulfur in the feed wasremoved as sulfur dioxide gas. The oxidation of the sulfide mineralmixture containing the FeSO -H O resulted in the removal of about 47% ofthe total sulfur, resulted in the production of a sulfide mineralcalcine containing only those sulfide compounds of iron and thenon-ferrous metals which are stable at temperature below the meltingpoint of ferrous sulfide and, in addition, resulted in the production ofsufficient iron oxide in situ to produce an activated calcine having amol ratio of sulfur to iron of less than unity when treated according tothis invention.

The second half of the above sulfide mineral mixture was then roasted ata temperature of about 800 C. in the presence of a generator gascontaining about 50% hydrogen. This treatment resulted in the productionof hydrogen sulfide gas and a calcine similar to the first one butcontaining no iron oxide.

The sulfur dioxide and hydrogen sulfide gases were collected for furtherprocessing to either elemental sulfur or sulfuric acid.

The sulfide mineral mixtures resulting from each of the above roastswere then mixed together. The mixed prod-. uct contained suificient ironoxide to produce an activated calcine having a mol ratio of sulfur toironiof less than,

Content Assumed Weight compounds Component percent;

Lbs. Lb.-mols Copper Sulfur Insolubles Total The above sulfide mineralmixture was then heated to a temperature of about 800 C. in the presenceof a reducing gas containing hydrogen to remove the oxygen from the Fe Oand thereby produce metallic iron for activation of the sulfide mineralcalcine to produce an activated calcine in which the contained iron wassoluble in dilute sulfuric acid.

The activated calcine was then treated with dilute (about 10%) sulfuricacid. In the treatment the activated calcine was employed in sufficientexcess so as to completely neutralize the sulfuric acid leach solution.Hydrogen sulfide gas was driven off during this step and collected forfurther processing. The resulting residue, after the treatment of excessactivated calcine with dilute sulfuric acid, had the followingapproximate composition:

Content Weight percent Component Lbs. Lb.-mols Total The above residuewas then leached in excess recycled dilute (about sulfuric acid. Thesecond residue was removed by filtration and was found to haveapproximately the following composition:

Content Component Weight percent Lbs. Lb.-mols Copper Lead The aboveresidue was then sent to a lead smelter for recovery of the lead,copper, and precious metals. The solution resulting from the treatmentof the activated calcine with excess sulfuric acid was again neutralizedwith a slight excess of additional activated calcine. The 6 in ExampleI.

16 The actual products obtained from the sulfide mineral feed were asfollows:

Products Quantity Sulfur Iron (lbs) (lbs) (lbs) Zinc sulfide 127 39 6178 13 5 1, 770 690 620 S 02 gas... 1, 230 250 Total 3, 345 922 781 Theabove products represent a recovery of about 97.5% of the iron ashigh-grade iron oxide, about 90.5% of the sulfur in the form of gaseswhich could be converted to elemental sulfur at high efiiciency, andsubstantially all of the zinc, lead and copper in two sulfideprecipitates from which the metal content could be reaily andeconomically extracted by conventional processes.

I claim:

1. The process of treating sulfide minerals containing iron andnon-ferrous metals having an atomic ratio of sulfur to iron in excess ofunity to recover the contained sulfur, iron, and non-ferrous metalstherefrom which comprises causing the sulfide mineral particles tocontact one another in the presence of metallic iron which is present inan amount in excess of the excess sulfur associated with the ironpresent in the sulfide mineral at a temperature below the melting pointof the sulfide mineral for a period of time sufiicient to produce asulfide mineral mixture in which the atomic ratio of sulfur to iron isless than unity to render the contained iron sulfide soluble in dilutemineral acid, and leaching the sulfide mineral mixture with a solutioncontaining a mineral acid.

2. In the treatment of raw sulfide mineral mixtures containing iron, thecombined heating and leaching procedure which comprises heating thesulfide mineral mixture containing iron to a temperature below themelting point of the mixture, removing, in the gas phase, that sulfurwhich is displaced from the mineral mixture by said heat treatment,adding to the residual hot solids mixture metallic iron until theproportion of the total iron to sulfur associated with the iron in themixture exceeds the ratio of 1 atom of iron to 1 atom of sulfur, andagitating the hot mixture at a temperature below the melting point ofthe mixture until substantially all of the iron content becomes capableof reacting with dilute sulfuric acid to produce soluble iron salts andhydrogen sulfide gas, and leaching the sulfide mineral mixture with asolution containing sulfuric acid.

3. The process of claim 2 in which the raw minerals are initially heatedin the presence of non-oxidizing neutral gases, and the excess sulfur isremoved in the elementary form.

4. The process of claim 2 in which the raw minerals are initially heatedin the presence of reducing gases containing hydrogen, and the excesssulfur is removed as hydrogen sulfide gas.

5. The process of claim 2 in which a hydrogen reducible iron compound isadded to the mineral feed and the agitation is carried out in thepresence of reducing gases containing hydrogen to produce in situ themetallic iron required to adjust the atomic ratio of iron to sulfurassociated with iron in the product to a number greater than unity.

6. The process of claim 2 in which the raw minerals are initially heatedin the presence of gases containing oxygen and the excess sulfur isremoved as sulfur dioxide gas.

7. The process of claim 5 in which the hydrogen reducible iron compoundis produced in situ by heating the 17 raw sulfide mineral mixture in thepresence of oxygencontaining gases.

8. The process of claim in which the hydrogen reducible iron compound isiron oxide produced in situ by heating the iron sulfate added to the rawsulfide mineral.

9. In the treatment of raw sulfide mineral mixtures containing iron, thecombined heating and leaching procedure which comprises heating thesulfide mineral mixture containing iron to a temperature below themelting point of the mixture, removing, in the gas phase, that sulfurwhich is displaced from the mineral mixture by said heat treatment,adding to the hot residual solids mixture metallic iron until theproportion of the total iron to sulfur associated with the iron in themixture exceeds the ratio of 1 atom of iron to 1 atom of sulfur,agitating the hot mixture at a temperature below the melting point ofthe mixture until substantially all of the iron content becomes capableof reacting with dilute sulfuric acid to produce soluble iron salts andhydrogen sulfide gas, leaching the iron treated product with a dilutesolution of a sulfuric acid, collecting the hydrogen sulfide gasresulting from the leaching, and separating the solution of metal saltsfrom the insoluble residue.

10. The process of claim 9 in which the leaching solution contains acidin excess of that required to react with all of the acid soluble metalsin the iron treated product.

11. The process of claim 9 in which the leaching solution contains aciddeficient to that required to react with all of the acid soluble metalsin the iron treated product.

12. The process of claim 10 in which the solution of metal salts isreacted with hydrogen sulfide gas and the sulfide solids are separatedfrom the solution.

13. The process of claim 11 in which the insoluble residue resultingfrom the leach is reacted with a second solution containing acid inexcess of that required to react with all of the acid soluble metalscontained in the insoluble residue.

References Cited in the file of this patent UNITED STATES PATENTS981,451 McKechnie Jan. 10, 1911 1,834,960 Mitchell Dec. 8, 19311,892,999 Ralston et al Jan. 3, 1933 2,424,866 Udy July 29, 19472,617,724 Espenschied Nov. 11, 1952 2,746,859 McGauley et al May 22,1956 2,759,809 Aimone et a1 Aug. 21, 1956 2,778,727 Schaufelberger Jan.22, 1957 2,871,116 Clark Jan. 27, 1959 FOREIGN PATENTS 112,615 GreatBritain Sept. 19, 1918 188,865 Great Britain Nov. 23, 1922 OTHERREFERENCES Hachks Chem. Dictionary, 3rd edition, 1953, page 820,published by The Blakiston Co. Inc., NY.

UNITED STATES PATENT oFFicE CERTIFICATE OF CORRECTIGN Patent No,3,053,651 September 11, 1962 Patrick J, McGauley It is hereby certifiedthat error appears in the above numbered pat ent requiring correctionand that the said Letters Patent should read as corrected below.

Column 5, 1ine44, for the equation, "ZnSO +ZnS+FeSO read Z nSO+FeS=ZnS+FeSO column 11, line 31, for

"Te" read Fe Signed and sealed this 5th day of February 1963.

(SEAL) Attest:

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of Patents

1. THE PROCESS OF TREATING SULFIDE MINERALS CONTAINING IRON ANDNON-FERROUS METALS HAVING AN ATOMIC RATIO OF SULFUR TO IRON IN EXCESS OFUNITY TO RECOVER THE CANTAINED SULFUR, IRON, AND NON-FERROUR MELTTHEREFROM WHICH COMPRISES CAUSING THE SULFIDE MINERAL PARTICLES TOCONTACT ONE ANOTHER IN THE PRESENCE OF MELALLIC IRON WHICH IS PRESENT INAN AMOUNT IN EXCESS OF THE SULFUR ASSOCIATED WITH THE IRON PRESENT INTHE SULFIDE MINERAL AT A TEMPERATURE BELOW THE MELTING POINT OF THESULFIDE MINERAL FOR A PERIOD OF TIME SUFFICIENT TO PRODUCE A SULFIDEMINERAL MISTURE IN WHICH THE ATOMIC RATIO OF SULFUR TO IRON IS LESS THANUNITY TO RENDER THE CONTAINED IRON SULFIDE SOLUBLE IN DILUTE MINERALACID, AND LEACHING THE SULFIDE MINERAL MIXTURE WITH A SOLUTIONCONTAINING A MINERAL ACID.